Sounds like your have some corruption on the harddrive, I would suggest to boot the computer off the Windows CD and choose to go into Recovery Console and run the following command:
chkdsk c: /p
This will fix any disk corruption preventing you from booting.
Here is a reference to recovery console:
229716 Description of the Windows 2000 Recovery Console
You may have to go into bios and change the boot up settings to boot from CD first. Or you could try a repair install if Win 2000 offers that. Failing that a complete reinstall of windows 'may' do the trick.